General Notices. 185 



proved at Sheerness, will not touch it ; while pieces of the same wood, steeped 

 in corrosive sublimate, sulphureous acid, and other active solutions, were bored 

 through and through. Let our ships be built of good sound English oak, as 

 they formerly were, well seasoned under cover, and left on the stocks as long 

 as they conveniently can be allowed, and we shall hear no more of dry rot, or 

 wet either." (Sir John Barroiv's Life of Lord Anson, as quoted in the Mech. 

 Mag., vol. xxx. p. 336.) 



Employment of Mineral Tar, or Pyroligneous Liquor, for the Protection of 

 Walls of Masonry or of Mud. — When the walls are thoroughly dry, towards 

 the end of summer (having previously been either newly built or put into a 

 state of thorough repair), they are to be coated over, once, twice, or thrice, 

 with the tar. The last coat, immediately when put on, may be powdered with 

 sand; and this, when solidified, may be whitewashed. In France, earthen 

 walls, and the walls of courtyards and terraces, are treated in this manner, and 

 so rendered of great durability. (Annates des Fonts et Chaussees, as quoted 

 in the Frank. Jour., vol. xxii. p. 284.) 



Preserving Specimens of Plants, or of Organic Substances generally. — Dr. 

 Riddell of Louisiana has found that, by wholly extracting the moisture from 

 the specimens to be preserved, which he does by means of unslacked lime, and 

 then enclosing them in hermetically sealed cases, they may be exposed to the 

 light without in the slightest degree losing their colour. By carefully sur- 

 rounding fresh specimens of i?6sa gallica with fine powder of quicklime, in a 

 close tin box, complete desiccation was accomplished in a single day ; and the 

 flowers, when taken out, were found of their natural shape and colour; but stiff 

 and brittle from dryness. The rose or other flower or plant, insect, &c, so dried 

 is next put into a case (like a wax flower), with a pane of glass in front, and 

 the whole closed by means of putty so as to be perfectly air-tight. Specimens 

 of insects, fungi, fruits, &c, are effectually embalmed in this manner; but the 

 most practically important part of the discovery to the botanist is, that cacti, 

 and other succulents, may be perfectly dried in a few days, and afterwards 

 deposited in cases with glass fronts, with their form and colour perfectly pre- 

 served. The details at length are given in Silliman's Journal, vol. xxxv. p. 338. 

 — Cond. 



Phenomena observed in the freezing of Potatoes. — When frozen potatoes are 

 thawed, they frequently do not give a fourth part of the starch which they 

 give before being frozen. The cause of this, it appears, is, that the starch, 

 being contained in the cells, or vesicles which constitute the principal part 

 of the parenchyma of the potato, is set free by the operation of the rasp or 

 grater in grating them down for starch. When the potato has been frozen, 

 however, and is afterwards thawed, the cells are no longer firmly fixed in the 

 fibrous matter of the potato, and the grater has no longer any power to 

 tear them to pieces. This is a most satisfactory mode of accounting for the 

 deficiency of starch in frozen potatoes ; and it also affords a proof of the 

 great value of microscopical observation. See an important paper in Quart. 

 Jour. Agricult., vol. viii., entitled Studies in the Science and Practice of Agri- 

 culture, &c, from which we shall probably hereafter give an extract. In 

 the original paper, by the discoverer of this fact, M. Payen, the different 

 states of the cells are shown by drawings. 



Every one knows that the most mealy part of a potato is immediately 

 within the skin ; and M. Payen has discovered that by far the greater num- 

 ber of cells of starch are in that part of the tuber, and that there are com- 

 paratively few towards its centre. 



M. Payen also found that the freezing of the outer part of the potato, 

 and the subsequent thawing, cause that bitterness which is invariably 

 found in frosted potatoes. Before the potato is frozen, the bitter principle, 

 being contained in the skin, is readily removed by paring or peeling ; but, 

 when the structure of the parenchyma of the potato is deranged by freezing 

 and thawing, the bitter matter is communicated to the adjoining parts of the 

 potato, in consequence of their comparatively fluid state. 



Vol. XV. — No. 109, o 



